Lab 2: Nerve Action Potential and Conduction

Question 1

Why is the whole nerve potential biphasic?

Answer 1

conduction speed is different in different axons so the signal travels down the curve as a wave
- first peak as signal reaches first electrode
- cancels out when signal across both electrodes
- second peak (opposite direction) as signal crosses second electrode

Question 2

threshold

Answer 2

min voltage needed to get a response

Question 3

what happened as we shortened the time between two pulses

Answer 3

amplitude of second WNP decreased because more and more axons were in their absolute refractory period when the second stimulus occurred

Question 4

what factor determines the refractory period of an axon

Answer 4

properties of the Na channel (inactivation molecule)

Question 5

what factors account for the difference in conduction velocity in ex vivo nerves compared to en vivo ones, and between different nerves

Answer 5

temp, environment (ie hooked up to a system of electrodes), solution (nutrients, O2 etc), prepartion (damage), state of the animal it came from

Question 6

myelin

Answer 6

increases electrical conduction of an axon -> increases membrane resistance -> decreases ion leakage -> increases conduction velocity

Question 7

factors that effect conduction velocity

Answer 7

myelin (primary factor), nodes of ranvier, diameter

Question 8

lignocaine

Answer 8

low affinity Na channel blocker -> temporary local anaesthetic because blocks conductance along axon, but binds weakly, wears off

Question 9

effect of lignocaine applied between first and second electrodes

Answer 9

amplitude of first peak stayed relatively the same, second decreased over time because channels blocked locally, reducing transmission of WNP as here so less signal at electrode 2

Question 10

paralytic shellfish poisoning

Answer 10

irreversible Na channel blockers, death due to resp failure, have to keep on life support long enough for Na channels to be replaced